For Molly, computer play in a simulated world connected strongly with off-line play. It reinforced her desire to create fictional worlds of her own. And it helped sharpen her understanding of that creative endeavor. In evaluating the imaginative and creafive worth of childhood activities, of course, this is the gold standard: that reading or watching television, that trips to the theater, to art and science ce museuns, an and id yyes, that play with computer games should stimulate personal en...

Ownership on the Bitcoin blockchain is determined by a pair of cryptographic keys. The first, called the public key, resides in the blockchain for anyone to see. The second is called the private key, and its owner keeps it safe from view. The two keys have a special mathematical relationship that makes them useful for signing digital messages. Here’s how that happens: Helmut takes a message, combines it with his private key, does some calculations, and ends up with a long number. Anyone who...

Children learn very early (often as young as 2 years old) to
recite the number-word list in order (Fuson, 1988). But at
the beginning, the words are merely placeholders—children
recite the list without knowing what the individual number
words mean. Over time, children fill in the words with
meaning, one at a time and in order (Carey, 2009; Sarnecka
& Lee, 2009). The child’s progress on this front is called
their number-knower level, or just knower level. A child
who does not yet know ...